Insert keyframe for rigid body properties for object python script blender
You have to use the correct datapath.

bpy.context.active_object.keyframe_insert(data_path="rigid_body.kinematic",frame=100)



Select the object, make it active.
Enable the animated (rigidbody.kinematic) property and keyframe it.
Disable the animated property on the frame you want to have the object start simulating and keyframe it.


This script assumes there is an object called Cube in the active scene.



import bpy

obj = bpy.data.objects['Cube']

start_frame = 100

# make the object the active object
bpy.context.scene.objects.active = obj
obj.select = True
bpy.ops.rigidbody.object_add()


obj.rigid_body.kinematic = True
obj.keyframe_insert(data_path="rigid_body.kinematic",frame=start_frame)
obj.rigid_body.kinematic = False
obj.keyframe_insert(data_path="rigid_body.kinematic",frame=start_frame+1)


Look at the python tooltips.